Etirinotecan pegol: development of a novel conjugated topoisomerase I inhibitor

Overview of the New Bioactive Heterocycles as Targeting Topoisomerase Inhibitors Useful Against Colon Cancer

Colorectal cancer (CRC) is the third most common cancer globally, with high mortality. Metastatic CRC is incurable in most cases, and multiple drug therapy can increase patients' life expectancy by 2 to 3 years. Efforts are being made to understand the relationship between topoisomerase enzymes and colorectal cancer. Some studies have shown that higher expression of these enzymes is correlated to a poor prognosis for this type of cancer. One of the primary drugs used in the treatment of CRC is Irinotecan, which can be used in monotherapy or, more commonly, in therapeutic schemes such as FOLFIRI (Fluorouracil, Leucovorin, and Irinotecan) and CAPIRI (Capecitabine and Irinotecan). Like Camptothecin, Irinotecan and other compounds have a mechanism of action based on the formation of a ternary complex with topoisomerase I and DNA providing damage to it, therefore leading to cell death. Thus, this review focused on the principal works published in the last ten years that demonstrate a correlation between the inhibition of different isoforms of topoisomerase and in vitro cytotoxic activity against CRC by natural products, semisynthetic and synthetic compounds of pyridine, quinoline, acridine, imidazoles, indoles, and metal complexes. The results revealed that natural compounds, semisynthetic and synthetic derivatives showed potential in vitro cytotoxicity against several colon cancer cell lines, and this activity was often accompanied by the ability to inhibit both isoforms of topoisomerase (I and II), highlighting that these enzymes can be promising targets for the development of new chemotherapy against CRC. Pyridine analogs were considered the most promising for this study, while the evaluation of the real potential of natural products was limited by the lack of information in their work. Moreover, the complexes, although promising, presented as the main limitation the lack of selectivity.

Etirinotecan pegol in women with recurrent platinum-resistant or refractory ovarian cancer

Introduction: A PEGylated form of irinotecan, a topoisomerase I inhibitor, is now available in commerce; its safety and efficacy have been tested in platinum resistant/refractory ovarian cancer (PROC) patients. This novel agent is known as Etirinotecan Pegol (EP). EP, like irinotecan, exerts its action through its principal metabolite SN-38. Areas covered: This drug evaluation article focuses on the most recent investigations and clinical progress regarding EP, a long-acting polymer conjugate of irinotecan for the treatment of PROC. Expert opinion: EP provides prolonged and continuous exposure of SN-38 in tumors, when compared to its parent drug irinotecan. Results from phase II studies are comparable in terms of efficacy to other agents of proven use in PROC. A limitation of the use of EP is the schedule-dependent toxicities (mainly diarrhea and dehydration). In the future, EP could be investigated in association with other agents, even in attempts to restore sensitivity to other treatments. PROC remains a very difficult setting and EP might be a valid agent for patients with good performance status that have exhausted therapeutic options. In such a setting, participation in clinical trials is strongly encouraged.

Synthesis of a peptide-universal nucleotide antigen: towards next-generation antibodies to detect topoisomerase I-DNA covalent complexes

The topoisomerase (topo) I-DNA covalent complex represents an attractive target for developing diagnostic antibodies to measure responsiveness to drugs. We report a new antigen, peptide , and four murine monoclonal antibodies raised against that exhibit excellent specificity for recognition of in comparison to structurally similar peptides by enzyme-linked immunosorbent assays. Although topo I-DNA complex detection was not achieved in cellular samples by these new antibodies, a new strategy for antigen design is reported.

A multicenter, open-label, expanded phase 2 study to evaluate the safety and efficacy of etirinotecan pegol, a polymer conjugate of irinotecan, in women with recurrent platinum-resistant or refractory ovarian cancer

OBJECTIVE

Etirinotecan pegol (EP) is a novel polyethylene glycol conjugated form of irinotecan with documented activity in platinum-resistant ovarian cancer (PROC). We report the results of the expanded portion of a phase II study of EP in patients with PROC who received prior pegylated liposomal doxorubicin (PLD) or who were unable to receive it.

METHODS

This multicenter, open-label, phase II study evaluated EP q21d for PROC. The primary endpoint was objective response rate (ORR) by Response Evaluation Criteria in Solid Tumors version 1.0. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and safety. Patient populations evaluated included a modified intent-to-treat (mITT) group consisting of all patients who received at least one dose and with measurable disease and a primary efficacy (pEFF) group (subset of the mITT population who received prior PLD).

RESULTS

One hundred thirty-nine patients were enrolled. Of the 132 patients in the mITT group, 20 achieved an ORR (15.2%; 95% CI 9.5-22.4); median PFS and OS were 4.4 months and 10.2 months, respectively. In the pEFF group (n=104), 15 patients (14.4%; 95% CI 8.3-22.7) achieved an ORR; median PFS and OS were 4.4 months and 10.9 months, respectively. The most common grade 3/4 toxicities were diarrhea (20%), abdominal pain (17%), vomiting (14%), dehydration (13%), and nausea (13%). Severe diarrhea was reduced to 15% with strict adherence to screening and management guidelines.

CONCLUSIONS

This study confirms the activity and safety of single-agent EP in patients with PROC, including patients who received prior PLD. Further evaluation earlier in the disease course and in combination is warranted.

Enhanced Delivery of SN-38 to Human Tumor Xenografts with an Anti-Trop-2-SN-38 Antibody Conjugate (Sacituzumab Govitecan)

PURPOSE

This study examined the delivery of SN-38 to Trop-2-expressing tumors and assessed the constitutive products in the serum, liver, and small intestine in nude mice bearing human tumor xenografts (Capan-1 or NCI-N87) given a single injection of irinotecan (40 mg/kg; ∼ 0.8 mg/mouse, containing ∼ 460 μg SN-38 equivalents) or sacituzumab govitecan (IMMU-132), an antibody-drug conjugate composed of a humanized anti-Trop-2 IgG coupled site specifically with an average of 7.6 molecules of SN-38.

EXPERIMENTAL DESIGN

At select times, tissues were extracted and concentrations of the products measured by reversed-phase high-performance liquid chromatography (HPLC).

RESULTS

In serum, >98% irinotecan cleared within 5 minutes; peak levels of SN-38 and SN-38G (glucuronidated SN-38) were detected in equal amounts at this time, and no longer detected after 6 to 8 hours. IMMU-132 was detected in the serum over 3 days, and at each interval, ≥ 95% of total SN-38 was bound to the antibody. Intact IMMU-132 cleared with a half-life of 14 hours, which closely reflected the in vitro rate of SN-38 released from the conjugate in mouse serum (i.e., 17.5 hours), whereas the IgG portion of the conjugate cleared with a half-life of 67.1 hours. In vitro and in vivo studies disclosed IgG-bound SN-38 was protected from glucuronidation. Area under the curve (AUC) analysis indicated that IMMU-132 delivers 20-fold to as much as 136-fold more SN-38 to tumors than irinotecan, with tumor:blood ratios favoring IMMU-132 by 20- to 40-fold. Intestinal concentrations of SN-38/SN-38G also were 9-fold lower with IMMU-132.

CONCLUSIONS

These studies confirm a superior SN-38 tumor delivery by IMMU-132 compared with irinotecan.